Synchronization of pre-recorded audio tape signals of motion picture film

ABSTRACT

Apparatus for synchronizing sound on a film strip with the frames on the film strip, used where sound was first recorded separately from the film on a sound tape and at the same time pulses were also recorded on the sound tape, the repetition rate of which pulses correspond to the film speed in the camera when the film was exposed. The apparatus achieves synchronization by controlling the relative speeds of, one, a tape transport, which transport generates an electrical signal of the recorded sound and, two, the film speed of the recording device which is putting the electrical signal of the recorded sound on the magnetic sound track of the previously exposed and developed film. The control of the relative speeds of the tape and film is accomplished by comparing the repetition rate of pulses generated from the pulse record on the sound tape to the repetition rate of pulses which are generated by the film in the device which is putting the sound signal on the magnetic sound track.

United States Patent [72] Inventor 10* L. Colodner PrimaryExaminer-Louis R. Prince Pearl River, N.Y. Assistant Examiner-Denis E.Corr [2|] Appl. No. 773,465 Attorney-Charles E. Temko [22] Filed Nov. 5,1968 [45] Patented June 8, I971 [73] Assignee The Synchronex CorporationNew York, N.Y. I

ABSTRACT: Apparatus for synchronizing sound on a film [54]SYNCIIRONIZATION 0F PIKE-RECORDED AUDIO strip with the frames on thefilm strip, used where sound was TAPE SIGNALS OF MOTION PICTURE FILMfirst recorded separately from the film on a sound tape and at 2ClnirnlADrawlng Figs. the same time pulses were also recorded on thesound tape, the repetition rate of which pulses correspond to the film E003335170129 Speed in the camera when the mm was exposed. The p Gown/O4:paratus achieves synchronization by controlling the relative [so] new ofSearch 3 52/1 2 l9 speeds of, one, a tape transport, which transportgenerates an '1' electrical signal of the recorded sound and, two, thefilm speed 20, l79/l00,2 T

of the recording device which is putting the electrical signal of 5mcite the recorded sound on the magnetic sound track of the previ-UNITED STATES PATENTS ously exposed and developed film. The control ofthe relative 3 297 835 I 1967 C I d speeds of the tape and film isaccomplished by comparing the 3'429'640 2/1969 0 'P 200/ repetition rateof pulses generated from the pulse record on Mac 352,12 the sound tapeto the repetition rate of pulses which are FOREIGN PATENTS generated bythe film in the device which is putting the sound l,l6l ,130 8/l96lGermany 352/ 19 signal on the magnetic sound track.

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E598 @zE NEE SYNCIIRONIZATION OF PIKE-RECORDED AUDIO TAPE SIGNALS OFMOTION PICTURE FILM completed magnetically striped film, so that thefilm may be 0 projected in a conventional magnetic sound projector.

In my prior US. Pat. No. 3,297,835, dated Jan. 10, 1967, there isdisclosed a motion picture camera having switch means driven by the filmadvance mechanism of the camera in such manner as to create anelectrical pulse from an energy source, and transmitted to a remotepoint for use. The invention contemplates the use of a separate taperecorder, which is operated simultaneously with operation of the camerain such manner that two tracks of recording are simultaneously made, oneof which records the pulses referred to in synchronism with the exposureof individual frames on the film, and the other of which records thereceived audio signals on a separate parallel track. It is known in theart to subsequently project the developed film in synchronism with areplaying of the tape, utilizing the recorded signals to synchronize thetape and projector, but devices of this type have been difficult tosynchronize, and suffer from a disadvantage in that very often duringthe simultaneous filming and taping by the user, the tape has beenplayed back by the operator to assure himself that it is functioningproperly, or to check recording level, and in such case synchronismbetween the tape and the film is lost at the end of the filming of oneor more scenes. Since the average amateur motion picture load carries to30 such scenes, the maintenance of synchronism between tape and film forthe entire length of the film is not a practical matter.

The present invention contemplates the simultaneous photographing andsound recording, using a separate tape recorder which records bothcontinuous pulses corresponding to the exposure of individual frames andthe received audio signal. When the exposed motion picture film has beenprocessed, either by reversal or printing methods, it is subsequentlyprocessed for the recording of the audio signals from the simultaneouslyexposed tape by the application of a magnetic stripe along one edge ofthe film. Subsequently, the signals from the tape are transferred to themagnetic stripe on the film, on a synchronized scene by scene basisprior to return to the user. If desired, the film may be subsequentlyedited in the normal manner, since synchronization between sound andfilm is permanently fixed on a frame by frame basis. Subsequentprojection by the user requires no adjustments at the time ofprojection, thereby facilitating the use of the invention by thosepossessed of only ordinary skills.

The application of sound striping to previously processed motion picturefilm, and the subsequent addition of sound onto the magnetic stripe isknown in the art, and has heretofore been practices on a relativelylimited scale using relatively expensive, professional type equipment.In the case of relatively inexpensive amateur equipment, severalproblems have arisen which are not conveniently solved while remainingwithin the price range of such equipment. One problem arises from thefact that the synchronizing signal which is placed on one of the tracksof the tape recorder can not be out of the audible range as therecording capability of relatively inexpensive recorders usually limitthe upper and lower frequency response to this area. While placing asignal on one track, to prevent crosstalk, the synchronizing signal mustbe of a low amplitude.

Another problem arises from the fact that the speeds of eitherelectrically driven or spring driven inexpensive cameras are normallynot very constant, and the variation in size and length of impulsesgenerated by the cameras vary greatly. Other problems arise from thepresence of frequency variation of oscillator circuits in the taperecorder supplying pulse signals, wide variations of amplitude of thepulse signals, and

even missing information caused by poor electrical contact of the switchlocated within the camera, creating corresponding to apparently missingsprocket holes on the film.

lt is therefore among the principal objects of the present invention toprovide improved means which may be used by a commercial processor ofmotion picture film which enables the elimination of the above mentionedproblems.

Another object of the invention lies in provision of synchronizing meansused in conjunction with the transfer of tape signals to processedmagnetically striped film which will compensate for frequency andamplitude variations in pulse signals, and supply missing informationresulting from missing signals, based upon the frequency of receivedsignals.

Yet another object of the invention lies in the provision of improvedsynchronizing means of the class described, in which the cost offabrication thereof may be of a reasonably low order, thereby permittingconsequent wide sale, distribution and use.

These objects, as well as other incidental ends and advantages, willmore fully appear in the progress of the following disclosure, and bepointed out in the appended claims.

Briefly stated, the disclosed embodiment of the invention contemplatesthe filtering of the input pulse signals to compensate for distortion,and noise, and the supplying missing pulses using ring counter circuits.The film being recorded.

also supplies signals based upon the passage of sprocket holes, whichare fed to a separate ring counter circuit. Means is provided to comparethe signals received from each of two counter circuits, and tocompensate the speed of the moving tape to achieve propersynchronization.

In the drawing, to which reference will be made in the specification,FIGS. 1A, 1B, and 1C, are a schematic wiring diagram of an embodiment ofthe invention.

H0. 2 is a block diagram of the embodiment.

Before entering into a consideration of FlGS. 1A, 1B, and 1C, theoperation of the embodiment may be more readily comprehended byconsideration of FlG. 2. The processing of an individual roll of filmand accompanying sound tape involves receiving synchronizing pulses andthe audio record from the prerecorded tape, recording the audio onto amagnetically striped track on the motion picture film, and achievingproper synchronization of the audio information with the frames on thefilm. This is accomplished by comparison of the synchronizing pulsesfrom the prerecorded tape with the film speed information derived from afilm advance mechanism A, and using the result of this comparison toregulate the speed of the transport mechanism B. This will establish theproper relationship between the film and the tape at the start of afilming sequence and will maintain this relationship during theremainder of the sequence.

The prerecorded tape is played back on a standard tape transportmodified for use in accordance with the present invention. Themodifications include a means for controlling the speed of the tapedrive motor by electronic signals, and provision for the output of boththe audio and synchronizing tracks. The audio output is fed to therecording circuits of the film mechanism or device used to record theaudio onto the sound track of the film. The synchronizing output of thetape transport mechanism B in the form of audio pulses is routed to async pulse amplifier D.

The sync pulse amplifierD includes a number of circuits for theprocessing of the synchronizing pulses. These pulses are first amplifiedto the desired level. The pulses are then filtered for a specificrange'of frequencies, and noise reduction is accomplished bythresholding techniques. Further amplification at the output, suppliesthe drive required by the multivibrator E at a next stage. The syncpulse amplifier D also provides an output for monitoring of thesynchronizing pulses.

The multivibrator E consists of a basic free-running oscillator that iscontrolled by the signals received from the sync pulse amplifier D. Itprovides an output at the same rate as the synchronizing pulses. Anoutput will also be supplied by the free-running oscillator whenever afew of the synchronizing pulses are missing from the prerecorded tape.The result of this circuitry contained within the sync pulse amplifier Dand multivibrator E is that synchronization of the prerecorded tape andthe film frames can be maintained even though the synchronizing pulseshave been degraded with noise, amplitude and frequency variations, oroccasional missing pulses.

The output of the multivibrator E is fed through a waveshaping circuit Fto obtain a square wave, before application to a counter circuit G.Pulse signals which are proportional to the film speed are also fedthrough a similar shaping circuit H before reaching a separate countercircuit l. Both of the identical counter circuits are of a four-stagering type. An automatic resetting provision, described hereinafter, isadded to the basic ring counter circuit to correct for any timing lag(film or tape) and to prevent false speed control information from beingsent to the succeeding stages of the system. The counter circuits G andl provide outputs of specific voltage levels corresponding to theregistered count which is an indication of the relative speeds of thetape and film.

The outputs from each of the counter circuits are compared in adifferential amplifier J. From this comparison, signals are developedwhich are used to vary the speed of the tape transport mechanism B inmaintaining system synchronization. The basic speed of the tapetransport is also controlled by the differential amplifier 1. When thesynchronization is achieved, and no correction to the tape speed isrequired, this basic or reference speed will be sent to drive motor ofthe tape transport B, which receives a standardized line voltage from anexternal source. The differential amplifier J supplies additionalpositive or negative voltage for regulation.

The power supply K furnishes the various voltage levels required by thecircuitry. A control system L consists of the various rate andadjustments and the switching arrangements necessary to the operation ofthe system.

In this system, the tape mechanism 8 is slaved by the electroniccircuitry to the speed of the film advancement mechanism A which isrelatively fixed. Normally, during the process of recording the audiorecord onto the film sound track, the film mechanism A is manually setto a speed similar to that of the camera exposure speed and the tapespeed is made to follow the film advancement. However, the film could becontrolled by starting, stopping, and speed regulation by use of logicsignals derived from the basic circuitry.

Referring to the drawing, FIGS. 1A, 1B, and 1C, the device comprisesbroadly: power supply means 8, tape signal filtering and amplifyingmeans 9, a first ringing counter circuit 10, a second ringing countercircuit 11 and comparator means 12. A pulse signal from a prerecordedtape is inserted at input 13, and is subsequently transmitted tocapacitor 14 and to the base 15 of a transistor 16 where the same isamplified. The pulse will normally be a three kilocycle pulse of 100millivolt amplitude in a burst proportional to the speed of the camera.The signal then passes to a second amplifying stage at transistor 17. Aninductive coil 18 and a capacitor 19 comprise a tuned circuit whichallows all information not wanted and carried by the signal to be passedto ground, and allows only the three kilocycle amplified signal to passthrough a conductor 20 to a variable resistor 21 which determines thegain. The signal continues through a coupling capacitor 22 totransistors 23a. This stage constitutes a differential amplifier. Thesignal enters the base of one side 24 of the transistor 23 foramplification. The signal is also fed through a resistor 25 to atransistor 23a where it is again amplified l80out of phase. Bothamplified signals are driven through diodes 26 and 27 which clip thebottom half of the signal, and allow only the positive portion to beapplied to the base 28 of a transistor 29 which is used to isolate noisefrom the differential amplifier stage.

The signal is continued through a coupling capacitor 30 to transistor31a, 32, and 33 which comprise a multivibrator or stage, the frequencyof which is controlled by the input signal, and which maybe be manuallyadjusted by a variable resistor 33a. This circuit operates on the tapepulse signal after it has been filtered and shaped to more useable form,and supplies a stabilizing function even when some of the synchronizingpulses are missing or inadequate. Transistors 31, 31a, and 35 form amonitoring circuit of the multivibrator operation and transistors 37,38, and 39 apply wave-shaping. The resultant signal is applied through amechanical switch 40 and conductor 41 to the first ring counter 10.

Transistors 34a form a differential amplifier, and receive a signal fromthe multivibrator stage during the conducting period from transistor 35.A capacitor 36 allows a square wave, during the conducting period, to beapplied a transistor 37 which serves as a decoupling component to drivetransistors 38 and 39. The signal, now inverted, is applied through amechanical switch 40 and conductor 41 to the first ringing circuit 10.

This circuit operates on the tape pulse signal, after it has beenfiltered and shaped to more usable form, and supplies a stabilizedsignal, even where some of the pulses are missing or inadequate. Thefunction of the circuit is similar to that discussed in Pulse & DigitalCircuits, by Millman & Taub, pages 5257; and 505-506, McGraw-Hill, NewYork City, 1956. The circuit includes five silicon controlledrectifiers, 45, 46, 47, 48 and 49. As each is fired, correspondingresistors are allowed to conduct thereby giving variations in voltage ofonehalf volt per resistor to differential amplifier transistor 63.Transistors 50, 51, and silicon controlled rectifiers 51a a5lband 51cform part of an automatic reset circuit, referred to herein above, andbecome conductive when a loss of synchronization occurs between the tapesignal and the projector signal. The projector (not shown) which recordsthe audio signal on the developed film, (after magnetic striping hasbeen applied) is also provided with a pulse generating mechanism,similar to that in the camera. The pulse output is fed to an input 54,and could be directly compared with the output of the tape recorderringing counter, since the limitations of the tape recorder signal arenot normally present in the projector. However, i have found itconvenient to use a separate ringing counter to shape the projectorpulses to correspond to those of the tape recorder for convenientComparison. The projector signal is fed through transistors 56 and 57 tothe second ring counter element which also includes five siliconcontrolled rectifiers 58, 59, 60, 61 and 62. The signal exitingtherefrom is summed with the tape signal in a differential amplifier 63,and the differential output voltage is transmitted through conductors 64and 65 to be superimposed, negatively or positively through monitor andservo 66 on the tape recorder motor voltage to result in slowing themotor (not shown) separately supplied or speeding it above its normaloperation in order to achieve perfect synchronization with the film.

It will be observed that by use of the above described circuitry, thetape signal has been amplified and filtered to allow only wantedinformation to be passed. The amplitude of the signal is not critical,but durations of time are utilized to vary the speed of themultivibrator circuit. Should, for any reason, the original input signalbe too low, too distorted, missing, or saturated with noise, the circuitwill continue to provide the proper corrective information by utilizingonly those signals which were previously acceptable. lf for any reason,either the film or the tape slip by increments of one frame, the ringcounter circuits, because of built in memory effect, will correct forany period of slippage.

1 wish it to be understood that I do not consider the invention limitedto the precise details of structure shown and set forth in thisspecification, for obvious modifications will occur to those skilled inthe art to which the invention pertains.

lclaim:

1. In a film recording device for recording synchronized audio signalsupon a magnetically striped motion picture film by utilizing asynchronized pulse, previously recorded on tape, in synchronism with theexposure of individual frames on said film, the improvement comprising:means for receiving a pulsed input from said tape, means for receiving apulsed input said differential amplifier means for regulating the speedof said tape in relation to the speed of film advancement.

2. Structure in accordance with claim I, further characterized in theprovision of s second ring circuit receiving pulsed signals from saidfilm recording device, and having an output leading to said differentialamplifier means.

1. In a film recording device for recording synchronized audio signalsupon a magnetically striped motion picture film by utilizing asynchronized pulse, previously recorded on tape, in synchronism with theexposure of individual frames on said film, the improvement comprising:means for receiving a pulsed input from said tape, means for receiving apulsed input from said recording device corresponding to individualsprocket holes in said film, means for filtering synchronizing pulsesfrom said tape from unwanted noise, a ring circuit receiving filteredpulses from said tape and having a stabilized output of frequencycorresponding to the frequency of tape input signals, differentialamplifier means for comparing the output of said ring circuit with apulsed signal output from said film recording device and means, forutilizing the output of said differential amplifier means for regulatingthe speed of said tape in relation to the speed of film advancement. 2.Structure in accordance with claim 1, further characterized in theprovision of s second ring circuit receiving pulsed signals from saidfilm recording device, and having an output leading to said differentialamplifier means.